A pre-filled syringe is often used to deliver medicament into a patient by discharge of the medicament from the syringe.
Prior to discharge, the pre-filled syringe often contains the medicament in a dischargeable form or, alternatively, in a form requiring conversion to the dischargeable form. The conversion often involves mixing together medicament components initially maintained apart within the syringe.
Prior to discharge, the dischargeable form of the medicament is often contained within the syringe between a slideable syringe plunger and a distal inner end of the syringe defining a discharge orifice, the plunger sealing circumferentially against an interior wall of the syringe.
A seal may require force to be dislodged from the interior wall if static friction is substantial. If the force is applied by a longitudinal impulse, such as a push by an operator's thumb, the impulse may provide enough energy to dislodge the seal, but may also compromise the operator's control over the displacement of the plunger once the seal is dislodged.
With the syringe oriented distal end up, discharge of air from the syringe (“priming”) may be effected by displacement of the plunger toward the distal inner end. Priming drives the air out through the discharge orifice and a distally attached delivery needle, thus filling the needle with the medicament.
After priming, before initiation of delivery of the medicament, the needle is inserted into the patient. Delivery of the medicament is effected by further displacement of the plunger toward the distal inner end. An extent of displacement of the plunger toward the distal inner end determines a volume of medicament delivered to the patient.
Typically, the extent of the plunger displacement delivering the medicament (“delivery stroke”) is limited by the plunger “bottoming out” against the distal inner end. Bottoming out typically involves deformation of a pliant material of the plunger, often against the distal inner end, which may include a pliant material of a needle-penetrated distal stopper.
The extent of the delivery stroke and, thereby, the volume of medicament delivered are often sensitive to deformation of the plunger and/or the stopper. Extent of such deformation is often not reliably repeatable. Bottoming out may not provide a reliable delivery mechanism for low volume of the medicament.
Operator manipulation to effect stages of syringe operation—such as mixing, priming or delivery—impacts volume of medicament remaining in the syringe at initiation of delivery. Typically, there is little or no feedback indicating to an operator when, during the manipulation, pre-delivery stages have been completed and when to initiate delivery. Without such indication of progress of stages of syringe operation, medicament to be delivered may be lost before initiation of delivery. Alternatively, the volume of medicament remaining in the syringe after pre-delivery stages may exceed a desired delivery volume. For low volume delivery, such loss or excess of medicament may represent a significant portion of the desired volume.
It would be desirable, therefore, to provide apparatus and methods for low volume medicament delivery with improved reliability over bottoming out.
It would also, therefore, be desirable to provide apparatus and methods for increasing the operator's control over the plunger displacement while dislodging the seal from the container wall.
Also, it would be desirable, therefore, to provide apparatus and methods providing indication of progress of stages of syringe operation.